There is an old marriage joke, which goes as follows. It is important to find a woman who makes you laugh. It is important to find a woman who is dependable and reliable. It is important to find a woman who is loving and tender. And the most important thing - is that these three women never meet.

In most four-stroke engines today, you will find the following three fluids: combustible air/fuel, water/glycol coolant and motor engine. And like the joke above, it is vital that none of these fluids ever come in contact with each other.

What is a head gasket?

The “Head Gasket” is the component which is responsible for routing these fluids correctly and ensuring that there is no intermixing. The gasket itself is a ringed panel that is placed between the cylinder head and the engine block, and acts as a barrier to prevent the engine fluids from leaking into the cylinders. As such, the head gasket can be regarded among the most vital components in the combustion chamber.

In addition to functioning as a barrier to the cylinder, the head gasket blocks off conduits to the oil and water.

Head gaskets are the most over stressed gaskets in an engine, because they must deal with sealing a multitude of things at the same time. They simultaneously seal oil, coolant, and engine compression away from each other and the outside. When do they blow, they can fail in several different ways, and each failure will result in different symptoms.

Before we look at each of the individual possibilities, let us quickly discuss head gasket failures in general.

Signs of a blown head gasket

Due to its obscured placement between components in the engine, the head gasket cannot be examined without major disassembling work. That in turn means that it is hard to make a diagnosis on a gasket’s condition, but visual inspections are rarely useful at pinpointing head gasket problems anyway. The best way to diagnose a problem is to study the symptoms as they occur and have a knowledge of what they most likely mean. Common symptoms of a blown head gasket include the following:

1. External leaks of coolant from under the exhaust gasket
2. Overheating under the hood
3. Smoke blowing from the exhaust with a white-ish tint
4. Depleted coolant levels with no trace of leakage
5. Bubble formations in the radiator and overflow compartment
6. Milky discoloration of the oil

Not so fast…

However, certain signs, such as cooling mixing with engine oil, a misfiring engine and oil leaks, may all indicate a blown head gasket. But the truth is, anything from the coolant system to the combustion chamber may be the culprit.

What makes it all the more confusing is the fact that symptoms which resemble those of a head gasket failure may originate from other causes, and, in certain cases, a symptom many present due to multiple failures within the engine.

For example,

1. Overheating may be causes by a restricted radiator, which can worsen the farther you drive along.
2. The presence of coolant in the oil, often blamed on the head gasket, could be due to a fault with the intake gasket.

Symptoms such the aforementioned may or may not be due to a head gasket. An accurate diagnosis is very much dependent on the expertise of a skilled mechanic.

7 Ways a head gasket can fail

There are 7 ways in which a gasket can fail, each of which will be described below:

This one’s not as easy to spot as some of the others, especially if the leaking coolant dribbles to the ground while driving, or evaporates, and leaves little trace of where it is leaking. If a head gasket fails between a water passage and the outside of the engine, the cooling system will eventually run low on coolant. When the coolant level drops too low the engine will overheat.

If the head gasket fails between the cylinder and an oil gallery, compression will enter the oil system and pressurize the crankcase. Hot compression gasses will compromise the lubrication of vital bearings, such as the crankshaft main bearings.

The same failure will also allow the piston to suck oil into the cylinder, where it will be burned off as part of the combustion process. This will eventually cause a drop in engine oil levels and will also cause blue smoke from the exhaust from burning oil.

If the head gasket fails between an oil gallery and a water passage it will allow the engine oil and coolant to mix. This will result in contaminated oil (the white milky sludge or "milk shake" associated with a blown head gasket) and a compromise the cooling system.

If the gasket fails across the fire rings it can allow the compression to leak from one cylinder to the next. This causes a loss of compression, and sometimes allows exhaust gasses back into the intake, depending on cam timing. This sort of head gasket leak typically results in rough running, misfires, and a loss of power.

This type of failure is not as common as the others, but some engines are prone to the head gasket leaking between the cylinder and the outside of the engine. This allows some of the compression to escape out of the engine, causing a ticking noise at idle that can sound like an exhaust leak. You will also experience rough running, and a loss of power.

This one is easy to spot, and if the head gasket fails between an oil gallery and the outside of the engine you will be able to see the oil leaking down the engine.

While not as immediately dangerous as other types of head gasket failure it will still require repair as it will only get worse over time. Depending on how the engine is designed, this sort of leak may result in less oil pressure getting to an overhead camshaft. Keep an eye on the engine oil level and don’t let it run low.

If the head gasket fails between the cylinder and a water passage it will allow exhaust gases to enter the cooling system, resulting a pressurized cooling system and overheating. Often this presents itself as a radiator hose blowing off its fitting.

This, in turn, can result in a damaged radiator, hoses, and other cooling system components. This leak also results in a drop in coolant level, causing overheating.

The same failure will also allow coolant to get sucked into the cylinder, where it is then burnt off as steam, or white smoke out the tailpipe, and a sweet smell. The steam that is burnt off can also cause lead to damage in the catalytic convertor as it exits through the exhaust system too.

The trouble with ignoring blown head gasket symptoms

Many drivers will ignore the blown head gasket symptoms due to the costs associated with the repairs. The blown head gasket cost is so high because of the labour typically involved. The part itself is not terribly expensive, as parts go, but it’s placement in the engine mean that many hours of labour are required. The mechanic needs to start by disassembling the entire engine, which takes a great deal of time. Then he needs to make the repairs, and only then can he put it back together. Putting an engine back together is not quick work either, as it requires a high level of precision. The smallest error in the cylinder timing or other settings can result in misfires or future challenges.

However, ignoring to replace the head gasket may prove an even more costly mistake, because in many cases, blown head gaskets lead to further car trouble if you continue driving.

What starts as a coolant leak, for example, if not addressed, could lead to the following problems:

1. Damage to the catalytic converter
2. Leaks into the engine oil, which can ruin the engine
3. Erosion of lubrication
4. Overheating caused by mixtures of coolant and combustion gases

Furthermore, mixtures of hydrocarbons and coolant can cause corrosion, which in turn can damage various engine parts like the radiator and heater.

A final word on overheating

As described above, when the failure of a head gasket occurs between the cooling system and combustion chamber, the evidence is typically displayed by coolant loss and overheating problems.

The latter symptom can be especially troubling because overheating often only shows in fits and starts, such as when a vehicle has been on the road for some distance. However, overheating can also cause damage when it doesn’t become apparent, such as during short trips along slow roads.

For example, if you drive from your house to the nearby shops, your car might not exceed 60 Km/h for the trip. Therefore, the car won’t reach the higher speeds that would more likely agitate an overheating issue. Nonetheless, the problem will still simmer inside the engine, even if you don’t end up seeing the heat gauge spike or any smoke seep from the hood of the car.

In cars where overheating does not become readily apparent, damages caused by combustion gasses could include the following:

1. Damage to the cooling system
2. Failure of the radiator
3. Erosion of the hoses

In some cases, one such problem might send off a chain reaction, such as where cooling system failure spreads to the radiator. The trouble is both could be damaged by overheating regardless. When a car gets misdiagnosed or when the driver skimps on repairs, there might be one component that is already ruined and several others that are significantly damaged, but the driver might only want to replace the component that’s shot.

Consequently, the other weakened parts might soon fail as well, and this could negatively impact the newly replaced component. Often, problems such as these are triggered not from overheating, but by other causes.

One example would be a leak in the water pump, which could damage the cooling system and in turn make the engine overheat. As an example of the domino effect with these kinds of problems, the water pump could be replaced, only for the other issues to continue, worsen and ultimately ruin the new pump. Then again, a water pump replacement might fix the problem, but only temporarily. Sooner or later, the head gasket could collapse — its weakness having been initiated during the overheat. Simply put, overheating can often be the gift that keeps on giving.

No matter what the cause, as soon as you notice an engine temperature warning light in your car, we recommend that you cease driving as soon as possible. Operating an overheating engine can quickly lead to total engine failure! That would leave you with a very costly engine rebuild or engine swap to keep your car on the road